DE2529956A1 - METHOD AND DEVICE FOR COATING SHEETS OF SHEETS - Google Patents

Description

Method and device for coating sheet material webs

The invention relates to coated sheet material, particularly to the manufacture of microcapsule-coated paper for use in pressure sensitive Copier systems.

One such copier system, known as a transfer system, includes a top sheet, labeled CB, which is placed on top of the The underside is coated with microcapsules that contain a solution of a colorless color former, as well as a lower so-called CF sheet, which is marked with a acid-forming color reactive material such as a Is coated with clay, a phenolic resin or certain organic salts. For most applications it will also be A number of interleaves, so-called SFB sheets, are provided, each of which has microcapsules on the underside and is coated on the top with the acidic color reactive material. By writing or typing Pressure exerted on the leaves ruptures the microcapsules, causing the color former to dissolve on the next lower leaf is released and a chemical

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Reaction takes place, which leads to color formation from the color former.

Another copier system, referred to as a self-contained system ¹ , comprises at least one on the
Upper side sheet coated with both microcapsules and the acid-forming color reactive material. Applying pressure by writing or typing on such sheets in turn leads to breakage of the
Capsules, as a result of which the color former solution is released onto the neighboring color reactive material and the color of the color former is developed.

Like the microcapsules, the coating composition contains for the production of CB or CFB material as well as sheets coated with both components im generally a binder and a so-called scaffolding material. The latter represents a means of protection to premature

Breakage of the capsules, for example during storage or

to
when handling the bow /. The framework material is particulate. The particles carry the sheet under relatively light pressure, for example during handling or storage, and thus prevent the exertion of pressure on the microcapsules and thus their breakage. On the other hand, if high pressure is exerted, for example when writing or typing, the protective effect of the framework material is no longer sufficient to prevent the microcapsules from breaking.

The binder is used to improve the adhesion of the microcapsules and the framework material to the paper base.

In the copier systems mentioned, it is desirable that the material containing the microcapsules

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layering completely and evenly over the entire surface of the CB or CEB or with both Components coated sheets extends to ensure that the entire area of the corresponding Sheets is able to produce a copy. It is also for economic reasons It is desirable to have a low coating weight of the composition containing the microcapsules use. As will be explained below, the achievement of a complete, even coating is beneficial with a low coating weight at the same time entails great practical and economic problems.

It has hitherto been customary to apply coatings containing microcapsules to paper as aqueous dispersions with a low solids content and then to level the applied coating with an air brush. A coating composition with a low solids content, for example 18 % solids, allows the use of a fairly thick wet film which ensures complete coverage and, after removal of the water, results in the desired low coating weight. In addition, a reasonably flat coating is obtained, since the airbrush sizing results in a coating that tends to 'follow' peaks and valleys in the paper _; than filling in the depressions and leaving the bumps with a lower coating weight. However, the method described has a number of disadvantages. First, the use of a low solids coating composition means that large amounts of water must be removed from the coated paper web (a high solids coating composition cannot work satisfactorily with the

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Air brush can be applied because of their higher viscosity Brings flow properties of the mixture with it, which do not allow adequate measurement by an air flow). The speed at which the coating can be carried out is further influenced by the problem of 'fogging' limited, since the dosing air jet has the tendency to blow droplets of liquid away from the tissue, whereby a 'fog' arises, which is subsequently either on the paper, resulting in an uneven coating pattern leads, or can be knocked down again at the tip of the air brush, which increases the evenness of the metering air flow and thus leads to the formation of an uneven coating pattern. That Problem worsens at higher coating speed, because the pressure of the metering air jet is greater. With careful operation, these Difficulties are largely suppressed, which are indispensable when operating at high speed Represents requirement. The particles of the framework material also tend to be selectively blown away by the wet coating on the fabric when this problem has also been mastered to a certain extent by operating personnel who work accordingly can be. The coating with the air brush is also, so far known, only for paper webs up to a certain vat can be used effectively.

When trying to address the mentioned problems by using a push-button leveling system instead of the air-brush leveling system to] graze, | if it is difficult to find the desired combination of low coating weight and completely flat coating with a good coating image. To produce a complete coating, a

fairly thick wet layer can be applied, whereby

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however, a doctor will not normally be useful for applying a coating of low viscosity, e.g., below about 200 cP Brookfield. In contrast, a microcapsule mixture with a low solids content of, for example, 18 % solids has a lower viscosity. If a coating composition with a higher solids content is used to achieve a higher viscosity, this leads either to an uneven coating appearance or an uneconomically high coating weight has to be applied in order to achieve a uniform distribution after the removal of the water. The problem is exacerbated by the fact that the use of scraper order leads to a uniform, smooth surface, but at the same time provides an unevenly thick film, since in contrast to air brush or air knife application, the depressions in the paper are filled and the bumps, on the other hand, have a low coating weight.

It could be thought of increasing the viscosity in a simple manner by adding a thickening agent increase. However, a thickener does not increase the thickness of the wet film, making it uneconomical thick wet coating to ensure complete coverage would still be required.

The presence of particulate framework materials in the coating mixture leads to further problems the use of doctor coaters. The scraper can first selectively remove framework material that is then fed back to the coating tank with the excess covering removed by the scraper. as

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As a result, the viscosity of the coating composition increases in the coating tank, and the control of coatings with low weight is increasing as a result more difficult. This problem arises particularly when cellulose fiber flakes are used as the framework material used (cellulose fiber flakes are probably the most widely used scaffolding material so far, although other materials have also been specified for this purpose, such as corn starch, granular synthetic polymers and numerous mineral materials). The particles of the framework material tend also tends to cake beneath the inclined scraper, resulting in strips of low coating weight results in the coating. In addition, parts of the scraper can be released intermittently of the caked particles of the framework material lift, resulting in the formation of strips with excessively high Soling weight leads.

The invention is based on the finding that the aforementioned, previously with the application of microcapsules or microcapsules and particulate framework materials problems associated with compositions containing compositions can thereby be solved or largely eliminated, that the coating composition prior to coating is foamed.

The invention is accordingly based on the object specify a coating process that does not have the disadvantages mentioned and is based on the foaming of the

based.

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The inventive method for coating sheet materials with a coating composition containing microcapsules comprises the following steps:

Foaming the composition,

Applying the foamed composition to the web as well

Leveling the composition on the web to a desired coating weight by an im Ablation device in contact with the composition on the web. The coating composition can also contain a particulate framework material.

The invention also includes devices for coating of sheet materials with foamed coating compositions as well as paper which has been coated by the method according to the invention.

The application device is preferably a scraper, which is for example rigid or preferably flexible. A flexible scraper is understood to mean a scraper which is able to bend to the same extent in the direction of the path movement over the entire width of the cutting edge. The surface facing the paper web is correspondingly convex, the degree of convexity being such that the web moves tangentially to the scraper and the contact point of the web and the scraper is at the end of the cutting edge or at a distance therefrom. In contrast, the suction bends. rigid scraper to a small extent and normally touches the paper web with the edge.

The method according to the invention can of course be applied to scrapers of any flexibility, from so-called rigid scrapers that are in edge contact with the paper web, to scrapers that extend up to the tangential Bend the position sufficiently to the paper web. If necessary

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the scraper can be part of a so-called flooded nip inverted blade 'or a so-called bill-blade coater (cf. for example GB-PS 1 115 133) or a so-called double or twin-blade coater (see for example the GB-PS 1 373 998). To apply the foamed Coating composition on the paper web proved to be S ^ OitzdUse ^ vAuftragger ate, (fountain applicator, hereinafter referred to as the DUsenaui carrier device Dezeichy as particularly suitable, especially when the applicator * is an elastic scraper. Although it has proven advantageous to use a scraper or a sheet as the application device however, other suitable devices can also be used; suitable application devices are, for example a Meyer rod or the roller of a so-called Champflex coater.

The amount of air or other gases in the foamed coating composition can be within a wide range, for example from about 25 to 75 %. However, the proportion of air is preferably 45-70 %. represent lower limits for the usable air content; however, if the air content falls below the above lowest value, the aforementioned disadvantages of the conventional scraper coating reappear. The upper and lower permissible air content depends to a certain extent on the other parameters of the coating composition, for example the solids content, the viscosity and the other components.

The pesticide content of the coating composition has generally not been found to be critical as compositions within a wide range of the solid

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content can be applied with good results. The use of a foamed coating composition allows the use of compositions with a solids content higher than usual, for example with 50 % or more solids. It has generally been found advantageous to use a higher air content with high solids coating compositions.

Although the viscosity of the coating composition affects almost every coating step, it was found that the coating process according to the invention Can be used with excellent results for coating compositions of very different viscosities is, for example for viscosities of 200 35OO cP Brookfield, i.e. roughly in the same area as is normally used for doctor blade shelving in the paper industry. A change in viscosity can be achieved in the process according to the invention by suitable choice of the Air content can be achieved. Those used in the manufacture of the microcapsules and the coating composition Processes and materials are also important. For example, a coating composition with microcapsules made of gelatin and carboxymethyl cellulose (CMC) have a higher viscosity as a composition with urea • ■ formaldehyde capsules.

The mean Ease size of the foam and the bubble size distribution around the mean size influence the viscosity or coatability of the mixture. A close one Distribution of the bubble size around the mean bubble size is therefore preferable. The bubble size in the below Examples described used foamed

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Coating compositions are predominantly in the range 10-100 to operate at an average bubble size of about 50-50 / um.

The type of paper to be coated seems to approximate the properties of the coating produced the same way as with conventional doctor coating. The influence of the paper base the properties of the coating are well known and so will not be discussed further.

The inventive method can be used within a wide range of coating speeds, for example from about 250 m / min to about 725 m / min carried out, whereby the specified numerical values do not represent procedural limit values.

Numerous products can be used as foaming agents, but care must be taken that the frother does not react with the walls of the microcapsules. Such reactions can be achieved with gelatin / CMC capsules occur when synthetic foaming agents are used; natural frothers are appropriate for this and similarly structured capsules are preferred. Suitable foaming agents include the following water-soluble polymers: Polyvinyl alcohol (PVA), natural products, for example proteins such as gelatine * casein and soybean extract, Saponin and also for capsules with urea-formaldehyde walls synthetic, in particular nonionic, surface-active substances. The frothers listed are not necessarily all suitable for all types of microcapsules. It should also be noted that some coating compositions can be foamed satisfactorily even without the use of an additional foamer ^. So can beln & lelswelee use the binding agent itself

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generate a suitable foam. Examples of binders in this category are the proteins mentioned as well as polyvinyl alcohol.

The foamed dispersion can be prepared in any suitable manner. It was found that, Although microcapsules are easily broken by mechanical pressure when dry, they are an aqueous suspension microcapsules can be exposed to the high shear stress of numerous high-speed mixers or stirrers, without damaging the microcapsules to any significant extent. Such mixers can accordingly can be used in the device used for foaming. Two types of foam generating devices that which can be used in the process according to the invention are explained in more detail in the following examples.

The framework materials used in the compositions to be foamed can, for example, consist of Cellulose fiber flakes, granular starch particles, granular synthetic polymers, hollow or liquid-containing Capsules of larger diameter than the composition microcapsules or particulate mineral materials such as talc or pigments or other particulate materials are more suitable A size that has no emery-like properties and is easily incorporated into the mixture before foaming can exist.

The invention is explained in more detail below with reference to the drawing; show it:

Fig. 1 is a block diagram showing the general arrangement of a paper coating machine;

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Fig. 2 is a flow sheet showing the stages of coating as well as foaming in such a machine;

Figure 5 is a flow diagram of an alternative frothing device as

Fig. 4 is a diagram showing the type of adjustment of an elastic scraper to adapt to Coating compositions with various properties emerges.

The paper coating machine shown in FIG comprises an unwinding stage 1 in which the paper 2 is unwound from a roll 3. The paper 2 becomes through the rollers 4 to a scraper coating device 5, in which a foamed aqueous coating composition comprising the microcapsules Contains particulate framework material and a binder, is applied to the paper 2. After the coating has been applied, the coated paper 7 dried in a dryer 8 and then passes over the rollers 9 to a roller 10 on which it is in the Winding stage 11 is wound up again. The foamed coating composition is placed in a foaming device β is generated, to which two alternative embodiments are described below. the foamed coating composition is applied to the coating device fed through a line 6a, excess coating composition is passed through the line 6b returned to foam again.

Fig. 2: The web 2 of the paper to be coated is guided around the underside of a carrier roller 12, wherein an excess of coating composition 13 with

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a fountain applicator lh is applied. The coating is smoothed by an elastic shaver 15, which rests against the roller 12, a coating of the desired thickness being produced by scraping off excess coating composition. The coated web 7 then enters the dryer. The removed excess coating composition is collected in an inclined trough 29 and passes through a line 29a into a collection tank 17 for re-foaming and reuse.

The foaming of the composition according to the invention is described in more detail below. Fresh coating composition comes from a storage tank 16 in the collection tank 17, from where it is with a pump 18 in the Tangential inlet of a separator 19 is pumped before it reaches the wire of a paper machine; as Separator 19 is a commonly used one for cleaning the starting materials in papermaking Separator. Air is introduced into the separator at the bottom through a perforated pipe; the air line is denoted by 20. A flow meter 21 is switched on in the air line to display the amount of air introduced. With a valve 22 the introduction of air can be adjusted, of which the air content can be adjusted accordingly and thus depend on the viscosity of the foam produced. The mixture emerging from the separator 19 of the coating composition and air passes to a high shear mixer (e.g. Oakes in-line rotating shaft mixer). To this This creates a foam with large bubbles. The foam is then used to create smaller bubble sizes made finer by passing through an array of nozzles and foam tubes 25. The arrangement shown consists of three devices arranged in parallel, from

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each of which consists of a nozzle and a foam tube arranged in series. The foamed composition thus prepared then arrives at the spray application device 14 for application onto the paper web 2. One with A branch line 26 provided with a valve leads to a measuring cell 27 for the air content and thus allows the display and monitoring the air content of the applied composition. The one subtracted to measure the air content Coating composition becomes spring foaming and returned to the collection tank 17 by a line 28 for reuse.

In Pig. 3 shows an alternative development of the foam generating device which comprises a closed mixer 30 located in the line, for example a closed tank with a rotatable stirrer, in which an aqueous coating composition containing the microcapsules, binding agents and particulate framework material is foamed. The dispersion is pumped from mixer 30 with a pump J> 1 at a pressure of about 1.75-2.1 kgf / cm (about 25-30 psi) via feed tube 32 to inlet manifold 33 of a foam generator.

The foamed coating composition leaves an outlet manifold 3 ^ through an outlet pipe 35 and arrives at a dope applicator ~} 6 with which a cockroach with an elaetiecbai? working coater is connected. Excess coating composition is fed into a container 37 and fed with a Purape 38 through a pipe 39 to the mixer 30 for reuse. Further coating components can be used both in dry form and as a dispersion

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via a line 40 to the mixer j50 for dispersion in the recycled coating composition are fed. From a compressor 42 or the like. generated compressed air is fed to a metering device 4l through which a certain amount of air is introduced into the pipe 40 will. The amount of air introduced is displayed by the metering device 4l and at a desired value held.

In Pig. 4 shows an elastic scraper 43 resting on a carrier roller 44. The Säiaber is from a holding device denoted by 45 held. As such holding devices in the paper coating industry are generally known, the construction of the holding device 45 is not explained in detail. the Position of the holding device 45 and the position of the Scraping in the holder are adjustable so that the so-called scraper angle oc and the scraper length can be varied, as is also common in the paper coating industry. The blade angle ex is the angle between the tangent to the carrier roller at the point of contact of the scraper and the direction of the shepherd at the point at which he came out exits the holder. The scraper length is the distance between the end of the holder 45 and the end of the scraper . in a non-bent position.

Scraper angle and length can be adjusted appropriately depending on the composition to be coated will. It is generally desirable to adjust the doctor angle as the viscosity of the foamed coating composition increases to enlarge. The preferred Sohaber length, on the other hand, does not seem very different Viscosity depend; it is only desirable to adjust them for mixtures of higher viscosity

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(to reduce). The thickness of the scraper, on the other hand, is not critical and is usually of the order of magnitude from IO thousandths.

The invention is explained in more detail below with the aid of examples.

Examples 1-70

The examples relate to coating runs, which were carried out to illustrate the broad applicability of the method according to the invention, it should be shown that the method according to the invention is particularly applicable to

a) compositions with different air contents and viscosities,

b) compositions with capsules made of different wall materials,

c) compositions with different solids content,

d) the coating of different carrier papers,

e) the coating at different speeds,

f) the use of different coating weights as well

g) Compositions with different framework materials.

The results obtained are shown in the table below.

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Table I.

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Example coating composition Type

A A A

A A A

A A B B

B B B

B B B B

Viscose Coating Coating remark 1! 11 I! very good air strength (cP) management development image very good very good H Well weight excellent excellent t? Well g / m ² net net very good coating excellent 58 430 6.1 excellent management net net dizzy very good 57 520 6.8 speed very good 60 520 3.8 550 m / min Well 53 455 5.4 very good coating Well management. very good 59.5 457 5.4 dizzy 47.5 175 5.4 speed 57.7 515 6.2 725 m / min 63 610 5.8 59.5 550 6.4 55 700 6.4 50 500 7.0 55 850 6.0 65 156O 6.6 37 440 6.6 27 320 6.1 56 910 5.6 59 1120 6.9 62.5 9OO 6.7 62.5 700 6.7 56 6OO 6.4 70 I82O 7.0

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Table I, continued

22nd B. 70 1580 6.9 excellent PVA binder excellent
net foam ribbed
Paper from
38 g / m ² weight 23 B. 67 1080 7.4 Well PVA binder dd MG base, smooth
page 24 B. 55.0 1200 5.7 very good PVA binder moderate MG base, rough
page 25th B. 55 1200 5.9 It 1! PVA binder Well foam ribbed
Paper _p of
38 g / m weight 26th B. 55 1200 5.0 Well very good Scaffolding material
Wheat starch 27 B. 55 1200 5.5 dd Well 28 B. 55 I5OO 5.6 Tt moderate 29 B. 55 1100 3.7 moderate Well 30th B. 55 1100 3.5 It moderate 31 B. 57 IO7O 3.8 It dd 32 B. 52.5 520 4.9 dd very good 33 B. 61.5 530 5.6 Well 34 B. 64 640 6.7 very good 35 B. 66.5 625 6.4 η tt 36 B. 57.5 700 6.8 37 B. 53 44ο 6.9 38 B. 56.5 640 6.8 39 B. 54.5 520 7.1 40 B. 60.5 980 6.1 41 B. 62.5 820 6.2 42 C. 40 920 6.3 43 C. 55 1350 6.1 44 D. 62 2740 6.5 45 D. 61.5 3100 5.9 46 C. 66 l44o 6.9

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E. Tabel I, continued 8.0 very good 47 E. 50 880 7.6 n tr 48 P. 55 1000 7.9 Well 49 F. 50 1220 5.9 very good 50 F. 60 2200 6.5 moderate 51 F. 37 ΐγΟΟ 6.1 ti 52 F. 60 29ΟΟ < -a Well 53 F. 50 2100 6.4 t! 54 F. 53 2840 5.7 II 55 F. 62 3400 5.8 It 56 F. 57 29ΟΟ 5.3 moderate 57 F. 57 28ΟΟ 6.1 It 58 F. 60 3400 5.8 dd 59 F. 25th 1680 6.1 Well 6ο F. 53 3120 4.0 moderate 61 F. 70 286Ο 6.1 Well 62 F. 56 2200 β, Ο !1 65 F. 48 I76O 6.5 very good 64 F. 53 I6OO 6.1 excellent 65 F. 63 25ΟΟ 5.7 It ββ F. 59.5 2460 3.2 moderate 67 F. 57 2600 6.2 Well 68 F. 56.5 235Ο β, Ο very good PVA binder 69 G 50 256Ο 4.4 excellent PVA binder 70 51 2680 net

Unless otherwise stated under 'Comments' the paper base used was a sheet material of 49 g / m and conventional type used in industrial Generating CB arcs is commonly used; the coating occurred at a speed of

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250 m / min on a coating device on a pilot plant scale; with the exception of the coating compositions explained below of types E and F, casein was used as a binder and foamer.

In all cases, the foam was produced as explained in connection with FIG. 2; the coating was in all cases applied with a gun applicator and with the variation of the coating weight happened by changing the Schabeawinkel and the SdtBba? length accordingly. The viscosity was measured in all cases using a Brookfield viscometer at 100 rpm. In In some cases it has been found that at a given air content the same coating composition different viscosities occurred; as a reason for this, the influence becomes different The bubble sizes in the foam are viewed to a certain extent through manual control of the air content is conditional.

The designations used in the table correspond to the types of coating compositions the following compositions:

A - 18 % solids composition; Production of the capsules by coacervation from an aqueous mixture of gelatin, carboxymethyl cellulose and polyvinyl methyl ether-maleic anhydride copolymer (for the process, see Example 1 of GB-PS 1 053 935, where gum arabic is used instead of carboxymethyl cellulose);

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B - 23 pound pesticide composition, same Capsules as in Aj

C - $ 28 pesticide composition, capsules as in A;

D - 33lb pesticide composition, capsules as in Λj

E - Composition with 33 ¹ P pesticide content, capsule walls made of urea-formaldehyde resin;

F - composition with 38 * p pesticide content, capsules as in E;

G - composition with 46 ^c / o solids content, capsules as in E.

The coating compositions were as follows manufactured:

Tj

Dry weight

Capsules 82.2

Types A - D: _{Solka flakes l4j8}

Casein or PVA 3.0

Capsules 84.4

Types A-D: wheat starch 12.6

Casein or PVA 3.0

Capsules 81.5

Types E Solka flakes 14.7

Starch (as a binder) 3.8

(Jalan Eil, distributed by Laing-National Limited).

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In the compositions of types E and F, Triton X-I65 was also used as a foamer in an amount of 4 % active weight based on the total solids content of the mixture.

Foam-ribbed paper is understood to mean a paper described in GB-PS 329 409.

Some of the scraping parameters typical of the tests on which Table 1 is based are given below:

1) Composition type A

Foamed composition with 58 fo air and a viscosity of 430 cP, coated at 6.1 g / m ² ;

Scraper parameters:

Length: 36.5 nrni (1 '16 ")

Thickness: (thousandths) 10 Angle: 26 °

2) Type B composition

Foamed composition with 58 % air and a viscosity of 700 cps; coated at 6.8 g / m ;

Function parameters:

Length: 36.5 nrm (I ⁷ A 6 ")

Thickness: (thousandths) 10

Angle: 38 °.

3) Type C composition

Foamed composition with 67 fo air and one

Viscosity of 1640 cP; coated at 6.5 g / m;

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Scraper parameters:

Length: 3β, 5 mm

Thickness: (thousandths) 10 Angle: ² ^.

4) Composition type D

Foamed composition with 51 fi air and a viscosity of 2560 cP; coated at 4.4 g / m ;

Vision parameters:

Length: 25.4mm (1 ")

Thickness: (thousandths) 10 Angle: 52.5 °.

Example 71

The example relates to the coating of a paper web with a coating composition which had been foamed using the apparatus shown in FIG.

Two coating compositions were prepared; the microcapsules of one composition contained gum arabic, those of the other carboxymethyl cellulose as one of the wall-forming materials (the remaining materials were gelatin and the polyvinyl methyl ether-maleic anhydride copolymer).

The framework material consisted of cellulose fiber flakes, casein was used as a binder.

The composition was in all cases:

5 0 3 8 8 3/1019, ", _ _{1! TePEC} T _E D

- 24th - Parts 2529 956 Microcapsules 82, 2 1! Dry weight Cellulose fiber !! 14, 8th Tt dd Casein 3, 0

This was followed by each of the coating compositions performed the following procedure.

The coating additive was made to have a pesticide content of 18 % and the pH was adjusted to above pH 10.5 with sodium hydroxide solution.

The coating mixture was in a foaming device as shown in Fig. 3 foamed to the desired air content. The air content of the foam was monitored with a device with which the hydrostatic pressure generated by a foam column was measured, the height of which was controlled by an overflow weir.

While the coating was being carried out, there was no increase in the contaminant content of the coating composition established.

The foamed coating composition was applied with a nozzle applicator to a Paper web applied, excess coating composition being removed with an elastic scraper became.

A comparative experiment using a non-foamed coating composition was also made carried out, which was applied with a roller application system with subsequent air brush.

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The coated paper was then in the manner described under Comparative Example 1 on his functional properties tested; the results obtained are shown in Table II.

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LO CO Γ0 C \! LD CM

TABLE II

Wall-
material assignment
system VoI-Ji
air Viscosity cP
(Brookfield Spin 3
at 100 rpm) Coating
conditionally 2
weight g / m Calender-
Intensi
activity % * Lubricant
firm
speed % * Rubber-
arabic around
Carboxy
methyl
cellulose Nozzle application,
roller
Nozzle application,
roller ??
46
41
48 600
290
250
305 6.0
7.0
4.6
6.1 62
66
64
52 § ⁹
85
88
87 Rubber-
arabipum Air brush
Coating un-
eo dreams 50 6.0 63 87

Tests described in Comparative Example I below.

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The similarity of the functional properties in the above examples, as well as the lack of an increase the solids content of the coating mixture in the recirculation circuit prove that in these cases there is no accumulation of cellulose fibers under the doctor. The paper produced showed an even distribution of the coating and had a flat sheet surface.

Example 72

A coating mixture was produced with the following composition:

Microcapsules 82.2 parts by weight dry weight cellulose fibers 14.8 "" " Casein 3.0 "" "

Sodium hydroxide 0.4 """; (20 # solution)

the solids content was 24.5 % *

The mixture was foamed as in Example 71 to foams with 48 and 58 % air content. The foams were applied to a paper web with a nozzle applicator, excess coating being removed with a flexible scraper. The coated paper thus prepared had a good coating image and a good smoothness. The paper was tested for its functional properties; the results obtained are shown in Table III.

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Table III

Viscosity OP % Coating Calender- Lubricant (Brook- air management Intensi firm field spindle 3, weight activity % * speed % * _t 100 rpm) 48 g / m ² 260 58 6.2 63 88 970 6.0 58 89

Carry out the tests as in the following comparative example I.

Example 73

A coating mixture of the same formulation as in Example 72 with a solids content of 23 % was prepared. The mixture was foamed using the system described in Example 71 to an air content of 54 %. The viscosity was found to be 470 cP. The foamed coating mixture was applied to the paper web with a roller applicator, excess coating being removed with a flexible doctor, whereby a coating weight of 6.3 g / m 2 was obtained. The coated mixture gave a calender intensity of 60 % and a smear resistance of 86 %.

Comparative example I.

To explain the functional properties of

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Papers coated by the process according to the invention are shown in Table IV below, test results with regard to the calender intensity (CI) and the smear resistance of papers specified after one of the examples in Table I or obtained by conventional methods.

In each case the composition contained casein as a binder, cellulose fiber flakes as the framework material and capsules made from gelatin / carboxymethyl cellulose / polyvinyl methyl ether-maleic anhydride copolymer; a flexible scraper was also used.

TABLE IV

Solid
salary assignment
procedure Coating
tungsge _r
weight g / m ' Calender-
Intensi
activity % Lubricant
firm
speed % 18 % Roller / air brush 5.5 56 89.6 25 % Roller / scraper
(foamed) 6.5 49.4 90.0 25 % Roller / scraper
(unfoamed) 5.4 51.4 74.0 25 % Nozzle cover / scarf
(foamed) ^{) he} 6.4 45.5 87.0 25 % Nozzle application / scarf
(unfoamed) ^{> he} 5.7 47.0 77.4

From the results obtained it can be seen that the papers produced by the process of the invention properties comparable to those of conventional air brush coating have produced papers, and that the paper coated according to the invention are useful have functional properties. The two examples

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le that relate to the use of a flexible scraper relate with an unfoamed composition, however, provide unfavorable in terms of lubricity resistance Results showing that the framework material did not adhere sufficiently and evenly to the paper had been applied.

The above-mentioned calender intensity test serves as a standard test for pressure-sensitive copier products and relies on a strip of capsule-coated paper on a strip of one having a co-reactant coated paper (e.g. CF paper) and the strips placed one on top of the other while exerting sufficient pressure to break the capsules (for example 15 kgf / cm, 83 lbs per linear inch) through a calender. The intensity of the printed image obtained after 48 h as well as the substrate are then with

measured with an opacimeter and the so-called calender intensi- ■ 1- ·· + - ι reflectivity of the print image _1nn . ^ ^{zaz axs} reflectivity of the background ^{x iUU given in} *. The lower the value of the print intensity, the more intensive the print or copy.

The smear resistance test is also a standard test for pressure-sensitive copier products and is used to determine the resistance of the capsules to premature breakage; a sheet loaded with a weight and coated with a co-reactant is drawn over a sheet coated with capsules and the reflection and background for the copy obtained on the sheet provided with the co-reactant is determined. As with the kaiander intensity, the result is given as a percentage. In terms of smear resistance, however, the higher the result, the better the resistance to premature breakage.

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Verglelchsbelsplel II

As mentioned earlier, the use of the doctor coating technique results in an unfoamed coating composition to a selective removal of framework material from the coating composition by the Scraper and subsequent return of the framework material into the container of the application device for the Coating composition with excess padding composition removed by the doctor. The example serves to explain this effect.

For initially identical foamed and non-foamed coating compositions with cellulose fiber flakes as the framework material, coating runs lasting 30 minutes were carried out in each case. The composition was applied with a nozzle applicator and removed with a flexible scraper. The initial pesticide content of the compositions was 23 tfo. After coating, the foamed composition showed no measurable increase in pesticide content, while the solids content of the non-foamed composition was 27 % . This increase in the solids content is due to the mentioned effect of selective removal of framework material and its return to the composition to be coated.

The example was repeated using wheat starch as the framework material instead of cellulose fiber flakes, again an increase from 23 to 27 % pesticide content being observed in the case of the non-foamed mixture during the

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The solids content of the foamed mixture remained unchanged.

Comparative example III

The example serves to illustrate the fact that the selective removal of framework material using a non-foamed coating composition occurs.

A composition of type B was used and used with a nozzle applicator and a rigid, freely hanging or drag doctor to remove excess coating composition in foamed and non-foamed form. Cellulose fiber curls were used as the framework material. The paper obtained was then tested for its smear resistance as described. For the foamed coating composition the smear strength was 89 % _t for the non- foamed composition 84%, from which it can be seen that the latter was more sensitive to premature breakage of the capsules, that is to say contained less framework material.

SO £ 883/1 0 1 9

Claims (8)

New patent claim Process for coating sheet material webs with a coating composition containing microcapsules, characterized by the following steps: Foaming of the composition, Applying the foamed composition to the web as well Ablating the composition on the web to a desired coating weight with one in contact with the removal device located on the web of the coating composition. 50S883 / 1019 "f *. 252S956 Claims > 4- o with a coating composition containing microcapsules, characterized by the following steps: Foaming of the composition: Applying the foamed composition to the web as Abrasion of the composition on the web to a desired coating weight with an induction in contact with the coating composition on the web 2. The method according to claim 1, characterized in that that the coating composition contains a particulate framework material. 3. The method according to claim 1 or 2, characterized in that that the removal device is a scraper. 4. The method according to claim 3> characterized in that the removal device is a blastic scraper. 5. The method according to claim 4, characterized in that the foamed composition with a nozzle applicator is applied to the web. 6. The method according to any one of claims 1-5, characterized in that the gas content of the foamed composition is 25-75 % . 5.09883 / 1 0 1 9 -54- 252S956 7. The method according to claim 6, characterized in that the gas content of the foamed composition 45 - 70/1 amounts to. 8. Coated sheet material made according to a Method according to one of the preceding claims. 509883/1019